Usually, an elevator's drive sheave and motor are arranged above the elevator car in a machine room. In buildings, where space is at a premium, machine rooms are not desirable.
Hydraulic elevators are driven by a piston which is usually disposed within a cylinder hole beneath the elevator car, thereby obviating the need for a machine room. However, building the hole and maintaining the piston therein is time consuming and expensive. Hydraulic elevators have other drawbacks relative to traction elevators: the rise of the car is limited by the length of the piston; the speed of travel is inferior; and the car weight is not offset by a counterweight making operation relatively inefficient.
Some elevators are driven by a linear motor having a tubular primary element disposed around a tubular secondary element. The linear motor does not require a machine room, as required by a traction elevator, and has no hole, as required by an hydraulic elevator. Also, linear motor driven elevators, relative to hydraulically powered elevators, are energy efficient, operate over a higher rise and are faster. Tubular linear motors typically utilize a secondary element which is hung from the top of the hoistway. At present, it is impractical to hang a secondary element over an extended rise.
UK Patent Application 2,237,555A to Toshiba shows an elevator driven by a linear motor having a flat secondary element and a flat primary element. The secondary element is affixed to the hoistway and avoids the problem of hanging the secondary element from the top of the hoistway. Some elevators have linear motors having highly conductive layers disposed upon the secondary elements thereof for increasing the efficiency of the motor.